300TDI misfiring at high revs

Hello All
I have a 1974 Range Rover which is running a 300TDI and Manual Box from a 1995 Discovery. (Was fitted with a Perkins when I bought it). I also run the Discovery fuel tank. Recently it started to missfire when I was on the motorway at ~70mph. I backed off to around 55 and left the motorway and it was ok. It misfired again pulling away from junctions just before a gear change (again when the revs were high). If I change gear early it runs fine - even under heavy load and when I can hear the turbo spinning.

Does anyone have any thoughs on what this is?

It always starts first turn of the key and runs well apart from this. The only other issue is that when I leave the house and it is cold it puts out a massive cloud of smoke when I go down the hill ~100yrds from the house. If I knock it out of gear its fine and once I have travelled 1/2mile it doen't smoke downhill. Its been doing this since I put the engine in so I dont think its related. I suspect the valve stem oil seals? There is no sideways play in the turbo vanes.

Thoughts I have are either the lift pump, the pipes coming out of the tank (they looked a bit corroded) or maybe the stop solenoid. (I do not run a sedimentor)

Thanks for your help
Jon

Here some pages from the defender manual may give some pointers
The smoking does sound like valve stem oil seals but lots of turbo problems cause smoke
Getting air in system can cause a misfire as can a lift pump not meeting fuel demand
Have you got a diesel fuel filter fitted and has this been changed recently

Thanks Steve. I put the fuel filter one about two years ago, but it's probably only done 1000 miles. It's worth changing it. I have ordered a new sender for the discovery fuel tank as there was definitely some corrosion on the pipes.
I did take it out again last week and it didn't miss at all then. It was only a short run though so never really got warm. I will read through what you sent and try the sender, filter and then look at the lift pump if that doesn't work.

Thanks again. Jon

The clear tube to FIP helped prove for me misfire wasn’t air in system
Cheap to to 8mm bore tube

I 'll give it a go. Thanks

Check the return at the injection pump isn’t blocked,

I'll check that.

I did check the intercooler hoses and they're all ok.

I have replaced the fuel pick up. I did need to drill out the rivits for the boot floor as there is no access panel, but it was relatively straightforward. When I took it out there was a large flake of rust partially blocking it. I guess it was from the fuel pipe just before the join as the tank is plastic. Hopefully this should have cured it.

As an aside, can you remove the cup/swirlpot/baffle that the pipe sits in the holes that it refills through when the diesel is low seem tiny (if I'm looking in the right place) and I might clean it out while I have access.

Thanks foe the suggestions and help.
Jon